Faculty Sponsor's Department:
SiC/SiC Ceramic-Matrix Composites (CMCs) have low density, high strength and high-temperature capabilities and are promising materials for hot section components in aircraft engines. Reaction Melt Infiltration (RMI) is often used to create dense CMCs, however this process is often associated with residual silicon in the matrix which limits the operating temperature. Previous work, primarily on the Si-Mo system, has shown that this problem can be mitigated by infiltrating the material with an alloy consisting of silicon and a rare earth metal instead of pure silicon. Here the rare earth metal reacts with silicon and forms silicides that have higher melting points. In the current work Differential Thermal Analysis (DTA), RMI, and Scanning Electron Microscopy (SEM) have been used to investigate selected alloy systems (Si-Y, Si-Zr and Si-Ti). The purpose of the research was to determine which rare earth metals are suitable for RMI and also to increase the understanding of which silicides or carbides a given alloy will form during RMI. The DTA measurements indicate that under adiabatic conditions the temperature change associated with the exothermic reactions can be in the order of hundreds of degrees Celsius, leading to the formation of higher melting point residual phases. The infiltrations were used to examine the impact of alloy composition on the climb and infiltration rate as well as to examine what silicide would form in a model system. The composition and microstructure of the resulting material was characterized using SEM.